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FairSeal Blockchain Notarization
x402
FairSeal Blockchain Notarization is a paid API for AI agents from x402.fairseal.io, paid per call via x402, $0.05/call, status unknown (last checked 2026-10-23).
Anchors an AI agent decision or audit record to Base mainnet via a Merkle batch, returning a receipt immediately and a full on-chain proof once the batch settles.
Price / call$0.05
Success—
StatusUnknown
How this service works
Anchor an AI agent decision or audit record to Base mainnet. Submit {schema, payload_hash (SHA-256 hex, 64 chars), metadata}; service queues into a Merkle batch and returns a receipt with pending_anchor status immediately. Full Merkle proof and on-chain anchor_tx available via free GET /v1/notarize/:receipt_id after batch anchors (within batch_threshold receipts or 120s). Include Idempotency-Key header to prevent double-charges on retry.
Output
An immediate receipt object with a receipt_id and pending_anchor status. Once the Merkle batch settles (within the batch threshold or 120 seconds), a GET /v1/notarize/:receipt_id returns the full Merkle proof and the on-chain anchor transaction hash on Base mainnet.
Example use cases
Audit trail for autonomous trading agent
“My trading agent just made a portfolio rebalancing decision — anchor it to Base mainnet as an agent_decision with agent_id 'trader-bot-7', decided_at '2024-06-10T09:30:00Z', the payload hash 'b4d2e1f3a5c7d9e0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4', and the decision_hash and input_hash from this run — I need an immutable on-chain record for compliance.”
Notarize audit evidence for regulatory review
“I have a piece of audit evidence I need notarized on Base mainnet — schema is audit_evidence, payload hash is 'c3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4', and the metadata includes the source system ID and timestamp. Can you submit it and give me a receipt?”
Record AI probe result for model monitoring
“Store a probe_record on the blockchain for my model monitoring pipeline — the payload SHA-256 is 'f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2' and the metadata includes probe_id 'probe-99' and run_at '2024-06-15T08:00:00Z'. I'll poll for the Merkle proof once the batch anchors.”
Technical details
Endpoint
POSThttps://x402.fairseal.io/v1/notarize?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a tamper-proof, on-chain record of an AI agent decision, audit event, or probe result anchored to Base mainnet with a verifiable Merkle proof. It is ideal for compliance, governance, and accountability use cases where you need an immutable cryptographic attestation retrievable later. Use the Idempotency-Key header on retries to avoid double-charges.
Side effects
- Invalid payload_hash format (not 64 lowercase hex chars) — 400 validation error
- Missing required metadata fields for the chosen schema (e.g. agent_id for agent_decision) — 400 error
- Payment failure or insufficient USDC balance — 402 Payment Required
- Duplicate submission without Idempotency-Key may result in double charges — use header to prevent
- Batch anchor delay beyond 120s in case of network congestion — proof may be temporarily unavailable
- Unknown schema type provided — 400 enum validation error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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